This invention relates to the general field of combustion systems and more particularly to a combustion system for a small gas turbine engine including variable airflow pressure actuated premix injectors.
In a small gas turbine engine, inlet air is continuously compressed, mixed with fuel in an inflammable proportion, and then contacted with an ignition source to ignite the mixture that will then continue to burn. The heat energy thus released then flows in the combustion gases to a turbine where it is converted to rotary energy for driving equipment such as an electrical generator. The combustion gases are then exhausted to atmosphere after giving up some of their remaining heat to the incoming air provided from the compressor.
Quantities of air greatly in excess of stoichiometric amounts are normally compressed and utilized to keep the combustor liner cool and dilute the combustor exhaust gases so as to avoid damage to the turbine nozzle and blades. Generally, primary sections of the combustor are operated near stoichiometric conditions which produce combustor gas temperatures up to approximately four thousand (4,000) degrees Fahrenheit. Further along the combustor, secondary air is admitted which lowers the fuel-air ratio (FAR) and lowers the gas temperatures so that the gases exiting the combustor are in the range of two thousand (2,000) degrees Fahrenheit.
It is well established that NOx formation is thermodynamically favored at high temperatures and the NOx formation reaction is highly temperature dependent. Operating the combustion process in a very lean condition (i.e., high excess air) is one of the simplest ways of achieving lower temperatures and hence lower NOx emissions. Very lean ignition and combustion, however, inevitably result in incomplete combustion and the attendant emissions that result therefrom. In addition, combustion processes are difficult to sustain at these extremely lean operating conditions. Further, it is difficult in a small gas turbine engine to achieve low emissions over the entire operating range of the turbine.
What is needed is a technique for decreasing the peak combustion temperature and limiting the residence time of the combustion products in the combustion zone to provide an effective means of reducing NOx emissions from gas turbine engines.
What is needed is an injector that allows operation of a combustion system over a wide range of operating conditions and minimizes emissions from the system.
In a first aspect, the present disclosure provides a turbogenerator system having a turbine mounted for rotation on a shaft, a motor/generator coupled with the shaft for rotation therewith, a combustor for combusting fuel and compressed air to generate combustion gases for rotating the turbine, a compressor providing compressed air, and an injector having at least one opening to admit the compressed air from the compressor, the injector connected to the combustor to inject fuel and compressed air into the combustor, a piston slidably covering the at least one opening providing a variable entry to the compressed air, and a pressure actuator associated with the piston and responsive to pressure in the combustor for determining size of the variable entry.